Volcanoes pose many threats to human life, both during eruptions and while dormant. More than 800 million people — one-tenth of the global population — live within 62 miles of an active volcano, making it a matter of public security to understand the risks.

Last week, a volcanic eruption forced the evacuation of the entire island of Ambae, which is part of the Pacific nation of Vanuatu. The island’s 11,000 residents were relocated to other islands, with authorities warning them of exposure to gas, ash fall, and acid rain.

Meanwhile, more than 140,000 people have evacuated Bali as scientists have declared a high alert for the eruption of Mount Agung, the highest volcano on the island. The country has instituted a seven-mile hazard zone around the volcano and is stocking up on supplies. More than 1,000 people were killed when Agung erupted in 1963.

Against this backdrop, a new study from the University of Bristol and published in the Journal of Applied Volcanologyexamines deaths caused by volcanoes with the aim of increasing public knowledge of volcanic hazards.

Sarah Brown, a professor of earth sciences at Bristol, and her team analyzed 500 years of data on volcanic fatalities. From 1500 to 2017, they found, more than 278,000 people have died from volcano-related hazards, amounting to 540 deaths per year on average.

The researchers collected information on the distance each person was from the volcano when they died, using scientific reports, media coverage, and volcano activity bulletins.

Nearly half of all volcanic deaths occurred within 7 miles of the eruption, but fatalities also occurred as far away as 106 miles. For those who were within 3 miles of a volcano, the most common cause of death was volcanic bombs or ballistics.

Between 3-10 miles, an avalanche of hot rock, ash, and gas known as pyroclastic flow was the most common cause of death, while volcanic mudslides, tsunamis, and ash fall are the main danger at greater distances.

Brown and her colleagues also examined the personal information of the victims. Most commonly, they were residents who lived very near to the volcano. But 561 tourist deaths were recorded, as well as 67 scientists (mostly volcanologists), 57 emergency responders, and 30 media personnel. In many cases, the victims were in known exclusion zones.

"While volcanologists and emergency response personnel might have valid reasons for their approach into hazardous zones, the benefits and risks must be carefully weighed,” Brown said in a press statement. "The media and tourists should observe exclusion zones and follow direction from the authorities and volcano observatories. Tourist fatalities could be reduced with appropriate access restrictions, warnings, and education."

Brown and her colleagues hope that their research will help other areas of the world plan and prepare for volcanic eruptions as Bali has this time around. Their location data could be particularly useful in predicting the impacts of eruption and knowing precisely where to establish exclusion zones.